The present invention concerns a wristwatch type watch, consisting of a display, such as an analog time display, an electronic circuit controlling the display, a time set stem, and at least two electrical contact elements, each alternately opening and closing one electrical connection in said electronic circuit when the time set stem is rotated and generating at least two electrical impulse signals which are transmitted to said electronic control circuit.
Numerous watches already exist, particularly wristwatches with analog time displays and electronic controls for the watch functions. In particular, British Patent Application Publication No. 2 070 815 and Swiss No. 637 521 describe such watches.
These watches comprise a time set stem which is partially square in section. Along the squared portion there are two cams which may be either square, rectangular, triangular, or elliptical in shape. The two cams are angularly offset from each other and attached to the stem in such a way that rotating the time set stem causes the cams to rotate. The cams are also located near two flexible conductive plates which alternately open and close electrical connections when displaced by the rotating cams. As a result, when the cams rotate, electrical impulse signals are generated, which alternate from being open to being closed, and vice versa, over a period of time.
The angularly offset position of the cams and the use of two electrical contacts make it possible to distinguish the direction in which the time set stem is rotating, in a manner known in the art.
The time set stem can generally be placed in different longitudinal positions in order to access various watch functions. For this purpose, the cams slide along the square section of the time set stem so that they always remain facing the conductive plates, regardless of the longitudinal position of the set stem.
This embodiment has several disadvantages. First, the square section of the time set stem must be large enough to hold the cams. Second, the cams require a considerable amount of space. This creates a particular problem with smaller watches such as ladies"" watches or very flat watches.
The cams must be positioned on the stem in a certain direction so that if the stem rotates in a given direction, the electronic circuit will not interpret it as a rotation in the opposite direction. Furthermore, given the size of the cams, assembly is clearly complex.
Because the cams must remain facing the conductive plates, a cam maintenance element must be located in a given longitudinal position, regardless of the longitudinal position of the time set stem. This element further complicates the assembly process.
Finally, in order for the cams to slide longitudinally along the time set stem, they must be attached to it with a certain degree of play. This introduces hysteresis in the electrical control signals.
This hysteresis must be electronically processed, which complicates the signal processing unit.
The present invention proposes a watch which overcomes these difficulties through the use of a time set stem that has no sliding cams, but allows access to its functions in the same manner as watches with sliding cams.
This object is achieved by a wristwatch such as the watch defined in the preamble, characterized in that at least one part of the time set stem includes at least one helicoidal portion cooperating with said electrical contacts to alternately open and close an electrical connection on the electronic circuit when the time set stem is rotated.
According to a first embodiment, the time set stem comprises two helicoidal portions.
According to a second embodiment, the time set stem comprises three helicoidal portions.
Said helicoidal portions are advantageously angularly offset at constant intervals.
According to a particular embodiment of the invention, the spaces between the spirals along each helicoidal element are constant.
The electrical contact elements are preferably separated by a given fixed distance (d).
According to a preferred embodiment, the spacing of the helices along the helicoidal elements, the angular separation between the elements, and the distance (d) separating the electrical contact elements are calculated so that the electrical signals formed by the alternate opening and closing of each electrical contact element when the time set stem is rotated at constant speed have a cyclical relationship ranging from 30% to 70% and are essentially equal to about 50%.
The spacing of the helices along the helicoidal elements, the angular separation between the elements, and the fixed distance (d) separating the electrical contact elements are calculated so that the electrical signals formed by the alternate opening and closing of each electrical contact element when the time set stem is rotated at constant speed are essentially in quadrature.
In one advantageous mode of the invention, wherein the time set stem can be placed in at least two different longitudinal positions, each electrical contact element cooperates with the time set stem zone that has at least one helicoidal portion at each longitudinal position on the time set stem, except a maximum of one set stem position.